Coplanar camera scanning system

ABSTRACT

A system for scanning objects having at least two linear array sensors, adapted to detect light input signals, is provided. A lens is optically connected to each of the linear array sensors, and are adapted to receive and transmit an optical image located in a respective lens field of view along a respective lens axis to the respective one of the at least two linear array sensor. A light source which generates an illumination stripe in general linear alignment with the lens axis across a depth of the field of view is provided. A cylindrical lens is positioned between the light source and an object to be scanned. The cylindrical lens adapted to collect, transmit and focus light from the light source to form the illumination stripe. This arrangement provides a wider system field of view with generally more uniform resolution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/982,820, filed Nov. 5, 2004, which is a continuation-in-part of U.S.application Ser. No. 10/676,834, filed Sep. 30, 2003, now U.S. Pat. No.6,856,440, which is a continuation of U.S. application Ser. No.09/810,204, filed Mar. 16, 2001, now U.S. Pat. No. 6,628,445, whichclaims the benefit of U.S. Provisional Application No. 60/190,273, filedMar. 17, 2000.

BACKGROUND

The present invention relates generally to optical scanning systems.More particularly, this invention relates to a scanning systemcontaining a camera using a coplanar light source.

Various optical scanning systems have been developed for reading anddecoding coded symbologies, identification of objects, comparison ofobjects, and measurement of objects. Each of these scanning systemsutilizes either a non-coherent or coherent light source. Lighting is oneof the key elements in obtaining good image quality. The intensity oflight needed for scanning is directly proportional to the transportspeed of the scanned object and the speed of the sensor. Generally, thefaster an image is to be acquired, the more light is needed. Until now,only high intensity sodium or halogen lighting was adequate to obtaincrisp images in cameras that focus over a significant depth of field athigh speeds. The light source is usually located off axis from thecamera and sensor detecting the light reflected from the object beingscanned.

In applications using sodium lamps as a light source, the lamps are usedto provide the illumination required by the camera detection means.These lamps provide an abundance of optical power because they are verybright and have a wide spectral range. There are, however, severaldisadvantages to sodium lamp light sources. First, due to their extremebrightness, sodium lamps can create an annoyance and possible hazard toworkers working in the vicinity of the scanning systems. Second, sodiumlights require a large amount of AC power, thus increasing productioncosts. Third, these light sources create a large amount of heat.Additionally, radio frequency interference can be created which canpresent operational problems to equipment in the vicinity of thescanning system.

The use of light sources such as LEDs presents several advantages oversodium and halogen lighting. LED illumination is a more cost effectiveand ergonomic method of illumination. The problem presented by LEDillumination is how to get enough light to the object that is beingimaged when focusing over a large depth of field. By eliminating themounting angle between the light source and the line of sight of thecamera lens, the reflected light is managed and a lower intensity lightsource may be used. Because LEDs can be energized almostinstantaneously, they can be de-energized when objects are not beingtransported within the field of view. This extends the life of the LEDsand also conserves power. Additionally, the power input to individualLEDs may be modulated and pinpointed to a desired area, such thatdifferent LEDs within an LED array may be energized at different levelsaccording to the desired application.

The use of a coherent or non-coherent light source which will providesufficient optical illumination to an object to be scanned, which usesless energy while alleviating potential problems of radio frequencyinterference or heat emission is needed.

SUMMARY OF THE INVENTION

Briefly stated, the present invention provides an optical scanningsystem which uses a light source to provide an illumination stripe thatis optically coplanar to a camera lens and light sensor for barcodereading applications. The light source may be coplanar to the lens axisand light sensor, and preferably is formed from LEDs or other low powerconsumption illumination sources. The coplanar design provides adequateillumination for a large depth of field at low speeds.

In another aspect, the invention provides a scanning system in which thelight source is shifted relative to the line of sight of the camera suchthat the illumination stripe remains coplanar with the camera line ofsight at the required depth of field. The light stripe profile comingfrom the array can therefore be narrow. The intensity of light requiredto illuminate an object over the depth of field is significantlyreduced, thus allowing for the use of an LED array or other low powerlight source.

In another aspect, the invention provides a plurality of off-axis lightsources to provide an illumination stripe on the object generallycoplanar with camera line of sight at the required depth of field.Different arrays of lights sources are energized according to the depthof field of the target object, allowing adequate lighting over a rangeof distances.

In another aspect, the present invention provides an optical scanningsystem which uses a light source to provide an illumination stripe thatis coplanar to at least two lenses and light sensors for imagingapplications. The light source is preferably optically coplanar to theaxes of the lenses and light sensors, and preferably is formed from LEDsor other low power consumption illumination sources. The design providesbroader imaging capability for wide width conveyors or higher densityimaging, along with more uniform resolution of the scanned symbologiesor images.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the coplanar camera in accordance with thepreferred embodiment of the present invention.

FIG. 2 is a top view of the coplanar camera in accordance with thepreferred embodiment of the present invention.

FIG. 3 is a front isometric view of the coplanar camera in accordancewith the preferred embodiment of the invention.

FIG. 4 is a side isometric view of a second embodiment of the inventionwith a movable array of light sources used in an off-camera lens axisorientation in accordance with the present invention.

FIG. 5 is a side isometric view of a multiple row large depth of fieldilluminator in accordance with the present invention.

FIG. 6 is an end view of a movable light source in accordance with thepresent invention.

FIG. 7 is an elevational view of another embodiment of the inventionincluding two optically coplanar cameras.

FIG. 8 is a perspective view showing the system field of view of thecoplanar cameras of FIG. 7 and the focusing of the illumination beamacross a depth of the system field of view

FIG. 9 is an enlarged isometric view of the scanning system of FIG. 7.

FIG. 10 is a bottom view taken along lines 10-10 in FIG. 7, showing thetwo camera lenses located in a generally optically coplanar positionwith the light source.

FIG. 11 is a top view taken along lines 11-11 in FIG. 7.

FIG. 12 is a side view of the coplanar camera system of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described with reference to the drawingfigures wherein like numerals represent like elements throughout.

Referring to FIG. 1, a coplanar camera scanning system 10 in accordancewith the present invention is shown. The coplanar camera scanning system10 preferably includes a light source 11, a camera lens 12, a focusingring 13 for the lens 12, a linear array sensor 14, a window 22, acylindrical lens 18, and a voice coil actuator 16. In the preferredembodiment, the light source 11 is comprised of one or more very highintensity LED arrays, although those skilled in the art will recognizeother suitable lighting could be utilized, such as lasers or a laserline generator.

The light source 11 is used to illuminate a surface of a target object,indicated by broken line 17. The emitted light illuminates the targetobject and is reflected back to the coplanar aligned sensor 14. Thecoplanar camera scanning system 10 is preferably used to read barcodeinformation from the scanned object. The coplanar camera scanning system10 preferably utilizes a CMOS linear array sensor 14 to detect the lightreflected from the object being scanned. In the first preferredembodiment a CMOS-based image sensor is referenced, but as those skilledin the art should know, any image sensor can be used, e.g., a CCD-basedimage sensor. The light reflected onto the CMOS linear array sensor 14is generated in the preferred embodiment by very high intensity LEDs 11.The preferred embodiment of the present invention utilizes red LEDswithin the array. As the technology regarding light sources advances,brighter, more intense LEDs can be used, including LEDs having differentwavelengths. Also low power semiconductor lasers can be utilized.

The LED array 11 acts as the light source for the coplanar camerascanning system 10. As shown in FIG. 2, in the first preferredembodiment of the present invention, the light source 11 is positionedparallel to, and in the same plane as the CMOS linear array sensor 14.Those skilled in the art should realize that the light source 11positioned in this manner is on-axis with the CMOS linear array sensor14. The light source 11 preferably comprises a plurality of LEDs inseries with each other, located on one or more circuit boards 31. Inthis embodiment, the coplanar camera utilizes two LED arrays to generatethe required amount of light. In this embodiment, the light source 11 ispositioned on each side of the camera lens 12. As should be clear tothose skilled in the art, the number of LEDs required for each lightsource 11 differs based on the size of the conveyor belt and requireddepth of field. The present invention preferably utilizes 50 LEDs ineach of the up to four arrays, totaling 200 LEDs. Alternatively, adesired number of low power semiconductor laser arrays may be mounted onthe circuit board 31.

The light emitted from the light source 11 is focused to a narrow“stripe” on the object using a cylindrical lens 18. This cylindricallens 18 is positioned parallel to and in between the light source 11 andthe target object. In the present preferred embodiment a Fresnel lens isused, but as those skilled in the art should realize, any optical lenscan be used in this application. As shown in FIGS. 1 and 2, thepositioning of the cylindrical lens in relation to the light source 11provides an illumination plane that can define a narrow “stripe” oflight anywhere within the depth of field. When the target object entersthis scanning field, the illumination from the light source 11illuminates the object. Due to the positioning of the sensor 14 relativeto the light source 11, the CMOS linear array sensor 14 detects the mostintense light provided by the light source 11.

As shown in FIGS. 1 and 3, the cylindrical lens 18 includes a centerslit 20. This center slit 20 permits the light reflected from the targetobject to return through the cylindrical lens 18 to the camera lens 12and then projected onto the CMOS linear array sensor 14.

In order to maximize the depth of field of the coplanar camera scanningsystem 10, the voice coil actuator 16 is coupled to the focusing ring 13of the imaging lens 12 to dynamically focus the image onto the CMOSlinear array sensor 14, based on a signal from a range finder 24. Thoseskilled in the art should recognize that there are many methods andapparatuses that can be used as range finders and for focusing. Thesignal received from the range finder 24 causes the voice coil actuator16 to move the camera lens 12 and focus the light reflected from theobject onto the linear array sensor 14.

Optionally, the invention may include a focusing mechanism 26 for thelight source to more accurately focus the emitted light onto a scannedobject. This enhances the image which is received by the camera lens 12and projected onto the CMOS linear array sensor 14. The focusingmechanism 26 is coupled to the light source 11, and dynamically movesthe position of the lens 18 with respect to the position of the lightsource 11. It should be noted that either the focusing mechanism 26 orthe light source 11, or both, may be moved to focus the light. Suchmovement, of course, depends on the distance of the object from theco-planer camera 10. This alternative embodiment keeps the intensity ofthe illumination stripe maximized at any distance, providing a cleanerimage for detection by the CMOS linear array sensor 14.

Referring to FIG. 4, a second embodiment of the present invention usesan off axis light source 40 which is located off the camera lens axisand the linear array sensor, as represented by lines 43. The off axislight source 40 illuminates a target object by directing a beam of lightonto its surface. However, the focused illumination stripe 44 iscoplanar with the camera lens axis 43 and the linear sensor array at therequired depth of field. The off axis light source 40 is preferably amovable array of LED sources 45 adapted to provide light to the targetobject. The invention, however, is not limited to this particularconfiguration or light source, as those skilled in the art willrecognize alternative light sources from those described, such assemiconductor lasers, may be used.

The light source 40 may be focused by using an optional lens 41. Thelens 41 may be any optical type lens, although a Fresnel lens ispreferred. A light source positioner 42, preferably in the form of acontrollable motor is connected to the light source 40 to allow movementof the light source 40. The positioner 42 is adapted to move the lightsource 40 based on a height of an object to be scanned, such that thefocused illumination stripe 44, 44′ is located on the surface of theobject. The object height may be determined by a range finder or othermeans.

As shown schematically in FIG. 5, the position of the off axis lightsource 40 is infinitely variable. Accordingly, the illumination stripe44, 44′, 44″ can be shifted to multiple positions depending on therequired depth of field along the axis 43.

Referring to FIG. 6, a third embodiment of the invention is shown whichincludes multiple arrays of light sources 51 which are located on one ormore circuit boards 52 placed off-axis to the lens 53 and the lineararray sensor. A range finder 50 is connected to the array of lightsources 51. The range finder 50 determines distance between the cameraand the target object. The distance data is sent to a controller whichthen powers on or off selected arrays of light sources 51 focused to acorresponding depth of field 55, 55′, 55″, 55′″ providing anillumination stripe 56, 56′, 56″, 56′″ coplanar to the camera lens axis57. The camera 53 and lens 54 detect the reflected light from theillumination stripe to read required data from the object.Alternatively, all of the light sources 51 may be activated to providethe desired illumination stripe at any depth of field, eliminating theneed for the distance to the target object.

Referring now to FIGS. 7-12, a fourth embodiment of a system 110 forscanning an object 105 in an object scanning area on a support surface107 is shown. The support surface 107 is preferably in the form of aconveyor or other moving surface upon which objects are carried. Thesystem 110 includes at least two linear array sensors 114, 115 to detectlight input signals. A sensor lens 112, 113 is optically connected toeach of the at least two linear array sensors 114, 115, with each of thelenses 112, 113 being adapted to receive and transmit an optical imagelocated in a respective optical field of view 124, 125 to the respectiveone of the at least two linear array sensors 114, 115. A light source111, similar to the light source 11 described above is also provided,and is preferably in the form of an array of LEDs or an array ofsemiconductor lasers, as shown in FIGS. 9 and 10. The arrays arepreferably linear and are directed toward a lens 118, which ispreferably in the form of a cylindrical lens or Fresnel lens, such asdescribed above in connection with lens 18. The light source 111 inconnection with the lens 118 produces an illumination plane 134 that hasa height (h) that extends over a depth of field 132 and a width (w) thatextends across the support surface 107 so that an illumination stripe isformed on a surface of the object 105 in the system field of view 130.The illumination plane 134, indicated by the two lines shown, and thesystem field of view 130 are generally coplanar over the depth of field132 in the object scanning area.

As shown most clearly in FIG. 8, the illumination plane 134 has atapering thickness that extends from a greatest thickness, adjacent tothe lens 118, to a narrowest thickness, adjacent to the support surface107. This taper will depend upon the focal length of the lens 118, butgenerally produces a high enough intensity illumination plane across theentire depth of field (h) so that the reflected optical image can betransmitted back to a respective one of the sensor lenses 112, 113.

Based upon an offset distance from the support surface 107 to the lineararray sensors 114, 115, the system field of view 130 has a generallyuniform resolution across the depth of field 132. This is in contrast tothe previously described embodiments of the invention where there is amore pronounced change in resolution from the shortest throw distancebetween the linear array sensors 114, 115 and a surface of an object 105to be scanned that has a height of about h, and the longest throwdistance for a short object. This is a function of the angle between thesupport surface 107 and the lines defining the respective fields of view124 and 125 of the linear array sensors 114, 115. The closer that thelines defining the fields of view 124, 125 come to vertical, the moreuniform the resolution across the depth of field, generally following asine function of the angle. This has a practical limit based upon aheight for the system 110 above the support surface 107 and the numberof linear array sensors 114, 115 which can be utilized.

A benefit of the system 110 is that the system field of view 130 has aneffective width factor (ew) that is greater than that for a singlesensor system. Still with reference to FIG. 7, for the system accordingto the invention ew>(w−s)h, where s is an offset distance at the heighth for a single field of view system, as represented schematically inFIG. 7. Utilizing the present embodiment of the invention with at leasttwo linear array sensors provides an offset distance s₂, as shown inFIG. 7, which results in an effective width factor ew=(w−s₂)h. In apreferred embodiment, s₂<0.8s, and more preferably is less than 0.7s,resulting in a greater effective width for scanning objects which arecarried along the support surface 107.

A further benefit of the system 110 is the ability to independentlyfocus each lens 112, 113 and sensor 114, 115 on a different throwdistance. Independent focus provides optimum focus on each surface wherea single item 105 has two or more surfaces that are at different heightsfrom the support surface 107 or where two or more items are present thathave surfaces at different heights from the support surface 107.

In the preferred embodiment, the linear array sensors are CMOS imagesensors and the light source lens 118 has a plurality of openings 120,121, as best shown in FIG. 9, to allow reflective light from a surfaceof the object 105 to return to the at least two of the linear arraysensors 114, 115 without being effected by the light source lens 118.The two linear array sensors may also comprise CCD image sensors, asnoted above.

Preferably, the system 110 has the linear array of LEDs or semiconductorlasers, as well as an axis of the light source lens 118 and theillumination plane 134 located coplanar with one another. Additionally,preferably the at least two linear array sensors 114, 115 are coplanarwith the linear array of LEDs or semiconductor lasers as well as theaxis of the light source lens 118 and the illumination plane 134. Whilethis is preferred, those skilled in the art will recognize that thecritical aspect of the invention is providing the system optical fieldof view 130 in a generally coplanar location with the illumination plane134 over the entire depth of field 132.

The use of at least two linear array sensors requires some overlap xbetween the two fields of view 124, 125 so that the known size barcodesor other labels can be read entirely by one of the linear array sensors114, 115, without the need for advanced logic for combining partialcodes read by different sensors. In a preferred embodiment, x equalsapproximately three inches, and the controller for the linear sensorarrays 114, 115 is preferably set to discriminate so that only a singlereading of one label is taken in the event that the entire label fallswithin both fields of view 124, 125 of the individual linear sensorarrays 114, 115. However, in some applications, multiple readings arepermitted and are passed on to a system controller for furtherevaluation in connection with the dimensioning and/or other datarelating to the object 105 on the support surface 107.

The system 110 can also be used in connection with mass flow conveyorswhere objects are side by side. In this case, the cameras areindependently focused and there is significant overlap of the two fieldsof view 124, 125 of the sensor arrays 114, 115 so that the two fields ofview each cover substantially the entire belt, less a width of thenarrowest object.

The system 110 can also be used in connection with scanning irregularshaped objects having varying heights. In this case, the cameras areagain focused independently and there is again a significant overlap ofthe two fields of view 124, 125 of the sensor arrays 114, 115 so thatthe two fields of view each cover substantially the entire belt. Thisprovides a higher performance system with a greater read rate.

The invention thus allows coverage over a wider support surface and/or ahigher density read by the linear array sensors 114, 115. Additionally,the use of at least two linear array sensors 114, 115 results in moreuniform resolution and less image distortion over a height h of thedepth of field 132.

Preferably all of the system components described above are packagedinside a read head assembly 150 which includes camera modules that housethe linear array sensors 114, 115, an illumination module that includesthe light source 111 in the form of LEDs or semiconductor lasers withthe focusing lens 118, and a controller for operating the sensors 114,115 and the light source 111. These are preferably mounted in a housing152 which can be constructed using any conventional means, but ispreferably made of sheet metal or polymeric or other metallic materials.

In the preferred embodiment, the lenses 112, 113 have a fixed focallength; however, it is also possible to provide an adjustable focallength lens for the linear sensor arrays 114, 115, in the same manner asdescribed above in connection with the prior embodiments of theinvention.

While the preferred embodiments of the invention have been described indetail, the invention is not limited to the specific embodimentsdescribed above, which should be considered exemplary. Further,modifications and extensions of the present invention may be developedbased upon the foregoing, all such modifications are deemed to be withinthe scope of the present invention as defined by the appended claims.

1. A large depth of field system located over a moving surface whichcarries objects to be scanned through an object scanning area,comprising: a linear array sensor adapted to detect light input signals;a sensor lens optically connected to the linear array sensor, the lensbeing adapted to receive and transmit an optical image located in anoptical field of view to the linear array sensor; a light sourcecomprising a housing having four side walls, at least one linear row ofLEDs located at a fifth wall of the housing, and a Fresnel lens that isspaced apart from and positioned to receive a generally unobstructedlight output of the LEDs located at a sixth wall of the housing,opposite the fifth wall, to produce an illumination plane that has aheight that extends over a depth of field and a width that extendsacross the field of view so that an illumination stripe is formed on asurface of the object traveling through the field of view; and theillumination plane and the field of view of the linear array sensor arecoplanar over the depth of field in the object scanning area.
 2. Thesystem for scanning objects of claim 1, wherein the linear array sensorcomprises a CCD image sensor.
 3. The system for scanning objects ofclaim 1, wherein the linear array sensor comprises a CMOS image sensor.4. The system for scanning objects of claim 1, wherein the linear row ofLEDs, an axis of the light source lens and the illumination plane arecoplanar.
 5. The system for scanning objects of claim 1, wherein theLEDs are mounted on circuit boards and are parallel to one another. 6.The system for scanning objects of claim 1, wherein a number of the LEDsutilized is dependent on the field of view.
 7. The system for scanningobjects of claim 1, wherein the LEDs extend across a fixed distance, theFresnel lens has a length that is at least generally equal to the fixeddistance, and the Fresnel lens includes a center slit through which theoptical image received by the linear array sensor passes.
 8. The systemfor scanning objects of claim 1, wherein a light source focusingmechanism focuses the illumination stripe at a desired distance.
 9. Thesystem for scanning objects of claim 1, wherein the at least one linearrow of LEDs extends generally across the field of view.